The Mitochondrial/Structural Core (9004) provides support to all of the individual projects in the program. All projects have utilized and continue to require populations of SSM and IFM for biochemical study. All of the projects require the assessment of myocardial and/or mitochondrial morphology for experimental data as well as for the assessment of quality control. The Core provides the following services to all the projects: . Isolation of subsarcolemmal and interfibrillar mitochondria from experimental hearts. . Samples of in situ myocardium and isolated populations of SSM and IFM obtained for light and electron microscopy--the latter includes transmission, scanning, and high-voltage electron microscopy-- will provide quality control. . Excess tissue and mitoehondrial samples are catalogued and stored for future use. . Experiments are entered into a common database available via network to all projects. Samples and the results of studies of respiration and biochemical endpoints are collated via database. Myocardial pathology is studied by light microscopy. Histochemical, immunohistological, and electron immunoeytochemical studies are performed on myocardium before and following ischemia and reperfusion. The frequency of myocyte apoptosis following ischemia and reperfusion is assessed.